Random time interval generator



United States Patent O f 3,521,171 RANDOM TIME INTERVAL GENERATORMichael S. Pinkert, 8811 Colesville Road, Silver Spring, Md. 20910 FiledApr. 7, 1967, Ser. No. 629,180 Int. Cl. H03k 5/00 US. Cl. 328-129 3Claims ABSTRACT OF THE DISCLOSURE A random time interval signalingdevice is presented which operates by driving an electronic counteruntil a signal is generated. When the signal is generated a secondarydriving means begins pulsing the counter and continues until the signalis turned off leaving the counter in a random state. The source of therandom time interval being the reaction time of the operator of thedevice.

BRIEF SUMMARY OF INVENTION The present invention relates to anelectronic device for generating signals at random time intervals.

According to the invention, an electronic counter is continuously pulsedby a low frequency input until the counter overflows at which time ahigh frequency input begins pulsing the counter and a signal isgenerated. The high frequency input continues pulsing the counter untilthe signal is turned off. When the signal is turned off, a random numberis left in the counter by the high frequency input and the low frequencyinput then takes over to pulse the counter again to the overflowcondition. By making the high frequency input substantially greater thanthe low frequency input, and, because the time taken to turn off thesignal will be diflerent at each overflow point, the number left in thecounter when the signal is turned off will vary giving the device thedesired randomness. The number of high frequency pulses generated isproportional to the time the signal is on which is a direct function ofthe reaction time required to turn off 'the signal. Hence, in thepreferred embodiment, where the operator is a human being, the variationin the human reaction time is effectively the source of the random timeinterval signal generation.

The device of the present invention provides an apparatus having fewelements and of relatively simple design to produce the desired signalat unpredictable random intervals. The apparatus requires a minimum ofmaintenance and calibration because of its lack of elaborate andexpensive high speed switching circuitry. A prototype model now beingtested, is no larger than a pocket sized transistor radio to facilitatethe handling and utility of the device.

If desired, rather than relying on the human reaction time to leave arandom number in the counter each time the signal is generated, it iswithin the scope of the present invention to provide a mechanical means,such as a heated metallic element, to cut oif the high frequency inputpulses and thereby maintain the random time interval operation.

There are many potential applications for this device including worksampling and quality control evaluation. For example, there is apractical need to signal observers, randomly and automatically, when tomake an observation or to take a sample. This would, in effect,eliminate the need for full-time observers who customarily use randomtime tables and consequently constantly watch the clock.

The manufacturer needs to know and keep a check on the quality of theitems he is producing, and, this quality check is most accurate whensamples are taken at random time intervals. The device of the presentinvention could be associated with an assembly line to take a sample,

3,521,171 Patented July 21, 1970 either manually or automatically, eachtime a random signal was generated. When samples are taken according toa definite sequential pattern, if there is any error present, it wouldmost likely be cumulative. The present invention provides a low cost,simple, convenient device to eliminate this potential error.

Even self work sampling is possible with the device of the presentinvention. For example, executives and other professionals can randomlysample how their time is used. Another obvious application is inpsychological testing.

BRIEF DESCRIPTION OF DRAWING FIG. 1 shows a functional block diagram ofthe components of the present invention; and, I

FIG. 2 shows a series of waveforms produced by the various components ofthe present invention.

DETAILED DESCRIPTION Referring to FIG. 1, there is shown a reset switch1 having an output 20 coupled to the C input of an enabling flip-flop orswitch 10. The enabling flip-flop or switch 10 is a binary storageelement having two states with the capacity to remember the last stateinto which it was forced even after the input signal has been removed.Clearing the enabling flip-flop 10 corresponds to forcing it to the 0state, and, setting implies forcing it to the I state. The C inputforces the enabling flip-flop to the 0 state as stated above. Thereforethe reset switch 1 is a momentary switch which is pushed to make contactand clear the enabling flip-flop to the 0 state when the random signalor audible tone is generated. The test/operate switch 2 has two outputs21, 22 corresponding respectively to test condition and operatecondition. The test output 21 is coupled to an AND gate 4 and theoperate output 22 is connected to an AND gate 5. Gates are used tooperate electronic switch circuits, actuate counters and in numerousother applications where an on-off type of signal is desired. The ANDgate requires that both inputs be present in order to generate an outputsignal. The AND gate 4 has connected at its second input 23 a signalproduced by the low frequency pulse generator 13. In the preferredembodiment the low frequency pulse generator would be capable ofproducing a continuous pulse at any one of several differentfrequencies. Hence, with the test/ operate switch 2 in the test positiona test input and input pulse from the low frequency pulse generator 13would each arrive at the AND gate 4 to induce an output in line 24coupled to the T input of enabling flip-flop 10. The T input correspondsto a toggle condition which forces the enabling flip-flop 10 to changeits state from whatever position it might be in. That is, whenevertoggle input T is actuated the enabling flip-flop is changed from either0 to I or I to 0. Since more than one input will not be present for anysignificant time there is no question as to what state the enablingflip-flop will be in.

The AND gate 5 has connected at its second input 25 the overflow pulsefrom the electronic counter 11. The

output 26 from AND gate 5 is coupled to the S input of enablingflip-flop 10. The S input forces the enabling flipflop 10 to the I statein the same way that the output 20 of reset switch 1 forces the enablingflip-flop 10 to the 0 state as hereinbefore set out. The electronicpulse counter 11 is a five (5) flip-flop register which counts thepulses received from either the low frequency pulse generator 13, or,the high frequency pulse generator 12 which pass through the OR gate 14.The OR gate 14, unlike the AND gates 4, 5, will produce an outputwhenever it receives an input from either the low frequency pulsegenerator 13 or high frequency pulse generator 12, or, both. Since thelow frequency pulse generator 13 operates continuously after powerswitch 3 is turned on, the OR gate 14 will always receive at least oneinput.

The low frequency pulse generator 13 has an output 28 connected to theOR gate 14. Similarly, high frequency pulse generator 12 has an input 29from enabling flip-flop and an output 30 to the OR gate 14. The OR gate14 has a single output 32 to the electronic counter 11. As statedbefore, the low frequency pulse generator 13 produces pulses at afrequency which can be preset by the operator at all times after switch3 is turned on. This generator is normally set several orders ofmagnitude lower than the frequency of the high frequency generator inthe order of from 1 c.p.s. to 1 c.p.m. The high frequency pulsegenerator 12 pulses at a fixed frequency when enabled by enablingflip-flop 10. This frequency is approximately -30 kc. Variations of upto in these frequencies have no critical effect on the operation of thedevice except for changing the tone frequency of the audible signal.

The electronic counter 11 generates two outputs. When the counter fillsup and overflows a counter overflow pulse is generated at output 33which is connected to input 25 of AND gate 5. As set out hereinbefore,when AND gate 5 is triggered by receiving an output from both theoperator switch 2 and counter overflow pulse, an output through line 26is directed to the S input of enabling flipflop 10 to force the enablingflip-flop to the I state. This output, of course, turns on the highfrequency pulse generator 12 also, and at the same time, an arbitrarilychosen output 34 at stage X of the electronic counter 11 is directed toAND gate 6. The arbitrary stage of the counter is used to drive thespeaker input and serves as an audio oscillator. The stage picked is anoutput which depends on the desired tone and is not critical to theoperation of the device. This arbitrary pulse, taken with the outputgenerated by enabling flip-flop 10 at output 35 in the I state, isjoined at AND gate 6 to produce an output 36 to the speaker driver 7 andspeaker 9. This latter output reproduces the audible signal remindingthe operator of the device that the high frequency pulse generator isnow pulsing the electronic counter 11, and, that the reset switch 1should be actuated to turn off the signal and start the cycle ofoperation again. Of course, at the sound of the signal the necessarysample or reading should be taken based on the function required of theoperator. The volume control knob 8 simply adjusts the intensity of theaudible signal produced when the counter 11 overflows.

In order to better understand the circuit above described, the generaloperation of the device will not be explained. The operator wouldinitially turn the power switch 3 to the on position. With thetest/operate switch 2 in the test position, the operator would thenpreset the mean time interval. In this state the Random Time IntervalGenerator, hereinafter called RADIK, will produce alternating intervalsof signals and no signals as a result of the T input of enablingflip-flop 10 switching back and forth from the O to the I state to turnthe high frequency pulse generator 12 on and off. FIG. 2 showsdiagrammatically the result of the different signals in waveformrelationship. FIG. 2(a) represents the power switch waveform when it isswitched from the off position to the on position. Of course, it remainson as long as the device is being used. FIG. 2(b) shows the test/operateswitch 2 which also produces a continuous signal in either of itsselected positions. Similarly, FIG. 2(6) shows arbitrarily the lowfrequency signal which operates continuously after the power switch 3 isturned on. Since the horizontal axis of the FIG. 2 diagram is a timeaxis, the timing relationship of the signals generated by the differentelements is clearly illustrated first by the enabling flip-flop switchwaveform of FIG. 2(d).

As pointed out above, when the test/operate switch is moved to the testposition, the T input of the enabling switch becomes actuated by aninput from line 24 to begin alternately shifting the enabling switchbetween the O and I states. Of course, during the time the enablingswitch is in the I state, an input is generated in line 35 whichcombines with the pulses from the arbitrary stage 34 of counter 11 toproduce an input at 36 to the speaker 7 as represented by the speakerwaveform of FIG. 2(f). Accordingly, the input 36 would produce anaudible signal each time the enabling switch moved to the I state. Bymeasuring the length of the no signal intervals with a stop watch andmultiplying this time by 16 the mean time interval can be determined.The mean time interval is then determined by multiplying by /z themaximum number of pulses required to overflow the counter. Since thepreferred counter is a five (5) flip-flop register, the determinationwould be based on the following formula:

Mean time interval= X (interval of no signal) 5 Mean time interval= X(interval of no signal) Mean time interval= 2 X (interval of no signal)Mean time interval=16 X (interval of no signal) Next the operator wouldmove the test/operate switch 2 to the operate position to beginproducing random time interval signals. With the test/operate switch 2in operate position, and the enable switch in the 0 state, the lowfrequency pulse generator 13 would direct pulses to the OR gate 14 andthrough output 32 to the electronic pulse counter 11. When the counteroverflowed an output would be generated at line 33 which would go to ANDgate 5 where it would be joined with an operate input 22 to produce anoutput at line 26. This output is connected to input S of enablingflip-flop 10 which forces the flipflop to the I state and produces aninput at 29 to start high frequency pulse generator 12. The highfrequency pulse generator then begins pulsing the electronic counter andcontinues to do so until the reset switch 1 is pushed to direct anoutput 20 to C input of enabling flip-flop 10 to clear the circuit. Thisstep would generate a signal at C to shift the enabling switch back tothe 0 state and turn-off the high frequency pulse generator 12. Further,since the low frequency pulse generator 13 runs continuously once thepower switch is on, it would still be driving the counter from the statethe counter was left in when the high frequency pulse generator wasturned off. Of course, this is the origin and source for the randomnessof the signals produced when the counter overflows. The electronic pulsecounter 11, of course, has the arbitrarily chosen output 34 at stage Xof the counter which directs an input to the AND gate 6. When theenabling flip-flop 10 is triggered to the I state as a result ofoverflow pulse 33, an output 35 is directed to the AND gate 6 whichcombines with the output 34 from counter 11 to induce the signal(audible) at 9 to indicate to the operator that he should perform thetask assigned him and then operate the reset switch 1. Since the ANDgate 6 requires both of the signals 34 and 35 to produce an output at36, the output produced will depend upon the state of the two inputs 34and 35,. Of course, as long as the enable switch 10 remains in the Istate, a constant signal is supplied at 35. Similarly, since the pulsegenerator 12 operates at a relatively high frequency (20-30 kc.) withthe enable switch in the I state, the input 32 to counter 11 under theseconditions would constitute high frequency pulses, and the output 34from the high frequency pulses being fed to counter 11 would besubstantially steady. Accordingly, the audible signal produced byspeaker 9 being responsive to the outputs at 34 and 35 would also benearly constant as long as the enable switch 10' remained in the Istate.

During the time the signal is on, a large number of pulses are fed intothe counter. Several counter overflow pulses will be generated beforethe reset switch is pushed, however, since the enabling flip-flopremains in the Istate until cleared, the additional overflow pulses haveno effect. The number of high frequency pulses generated is directlyproportional to the time the signal is on which corresponds to thereaction time of the operator.

When the operator pushes the reset switch 1 to clear the enablingflip-flop 10, the high frequency pulse generator 12 is cut off and thesignal, or audible sound from speaker 9, is turned oh. This allows thelow frequency pulse generator 13, which runs continuously, to again'begin pulsing the electronic pulse counter 11 from whatever state thehigh frequency generator 12 has left it in, to start a new cycle.

As stated hereinbefore, because the reaction time of the operatorvaries, the number left in the counter 11 when the high frequency pulsegenerator 12 is turned off after each cycle will be different to providethe random time interval signal desired.

FIG. 2 shows the different waveforms produced when various components ofthe device are actuated. FIG. 2(a) shows simply the on and off state,with FIG. 2(1)) showing the difference between test condition andoperate condition. FIG. 2(0) shows the low frequency generator pulsesand FIG. 2(d) shows the state of the waveform when the enablingflip-flop 10 is alternately actuated and cleared. FIG. 2(e) shows thehigh frequency input pulses which are constant in the order of from20-30 kc. FIG. 2(f) showing the signal generation waveform of speaker 9,is the same as the enable flip-flop waveform. FIG. 2(g) shows theposition and relationship of the counter overflow pulse and the resetswitch waveform as illustrated in FIG. 2(h).

It should be pointed out that that arbitrary output at stage X of theelectronic counter is chosen to produce a tone of the frequency at whichit is taken off. This particular frequency will be different dependingupon the conditions under which the operator is working.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. An electronic timing circuit for producing a random time signalcomprising, a low frequency pulse generator and a high frequency pulsegenerator, each having an output connected to an electronic counter,said high frequency pulse generator being responsive to the state of anenabling switch, wherein, with the said enabling switch in a firststate, only said low frequency generator pulses said counter until saidcounter produces an overflow pulse, said counter overflow pulseproducing a first input to said enabling switch for shifting theenabling switch to a second state wherein said high frequency generatoroutput supplies pulses to said counter while simultaneously said randomsignal is produced, and means for impressing a second input on saidenabling switch to shift the enabling switch back to said first stateleaving the counter in a random state and permitting only the lowfrequency generator to pulse the counter.

2. The circuit of claim 1 wherein said random signal is produced by thecombined signal from said enabling switch in its second state and anarbitrarily chosen output from said counter.

3. The circuit of claim 2 wherein said first input comprises thecombincd overflow pulse from said counter and the signal from an operateswitch, and the second input comprises the output from a reset switch.

References Cited UNITED STATES PATENTS 2,589,270 3/1952 Mayle 328129 XR2,832,044 4/ 1958 Bliss 328129 XR 2,941,152 6/1960 Gosslau 328l29 XR3,002,151 9/1961 Broderick et al. 32848 XR DONALD D. FORRER, PrimaryExaminer J. ZAZWORSKY, Assistant Examiner U.S. Cl. X.R.

